By rosebell
The factory acceptance test of the final TBM for DC Water’s Potomac River Tunnel has been completed.
In order to digging the southern leg of the Potomac River Tunnel in Washington DC, contractor CBNA-Halmar JV with its design partners Cowi and Hatch is due to operate TBM Emily.
The official activate of the cutterhead will be done by Led by CEO and general manager David Gadis and DC Water’s team that travelled to Herrenknecht’s factory in Germany.
According to Gadis: “Seeing Emily in action was a powerful moment for our team and underscores the scale and impact of what we’re building.It’s one thing to plan and design a tunnel boring machine, but watching it take shape reminds us why we do this work — to build a cleaner, healthier future for the district.”
While TBM Mary is scheduled to start excavation of the northern leg of the tunnel in early 2026,Emily will join her sister. The two machines are named after Emily and Mary Edmonson, two sisters who escaped slavery in 1848 by sailing down the Potomac River and then became prominent US civil rights figures. Emily is engineered for softer soils, while Mary is designed to cut through hard rock.
With the aim of transporting TBM Emily will now be disassembled and reassembled at the West Potomac Park site in spring 2026.
As a long-term initiative to decrease pollution in the Potomac River and Chesapeake Bay, the Potomac River Tunnel is part of DC Water’s Clean Rivers Program and the quantity of untreated sewer overflow that enter the river each year is almost 650 million gallons. Following completion, the 8.8km tunnel system will reduce overflow volume by 93% and cut the number of overflow events from 74 to just four in a typical year.
